The present invention relates to a fusible link and, in particular, to a fusible link of a cartridge type which is used to protect a power supply circuit for use in a vehicle or the like.
Power supply in a vehicle such as an automobile and the like is normally supplied from its on-board battery and, in order to protect the power supply against a short circuit accident or the like in various electric parts, electric wires and the like, there are provided various kinds of fuses. As a fuse in such a circuit requires a relatively large current, in order to minimize a contact resistance in a connecting portion as well as to secure positive assembly, there has often been used a fusible link of a cartridge type, the connecting terminal plate of which is screwed to an external terminal by use of a bolt and a nut.
Now, in FIG. 7, there is shown a fusible link having a conventional structure and, in FIG. 8, there is shown a fuse element which is applied to the fusible link (Japanese Utility Model Application Sho. 63-82347).
In other words, according to the conventional fusible link 1, simultaneously to when the fuse element 2 shown in FIG. 8 is assembled into a housing 3, a connecting plate 4 forming the fuse element 2 is projected externally of the housing 3.
The assembly or engagement of the fuse element 2 into the housing 3 is achieved in the following manner: that is, for example, there is prepared a U-shaped fuse element having a pair of connecting plates 4; the parts of the respective plate surfaces of the connecting plates 4 are cut and raised to thereby provide two elastic engagement pieces 6 and 7; there is provided in the inner wall of the housing a projection 8 which is shown in FIG. 9 and is disposed so as to correspond to the elastic engagement pieces 6, 7; and, the elastic engagement pieces 6, 7 are engaged with the projection 8. That is, when the fuse element 2 is assemble into the housing 3, the engagement pieces 6, 7 hold and support the side walls of the projection 8 between them.
In the above-mentioned conventional engagement method, one 6 of the engagement pieces 6, 7 prevents the connecting plate 4 from slipping off in the direction of an arrow I shown in FIG. 7 and at the same time the other 7 prevents the connecting plate 4 from slipping off in the direction of an arrow J shown in FIG. 7 and, therefore, the fuse element 2 can be properly fixed to the housing 3.
However, in the above-mentioned conventional structure, since the surface of the connecting plate is cut open in order to provide the elastic engagement pieces, as shown in FIG. 8, the sectional area x--x of the connecting plate, in which these elastic engagement pieces are provided, is smaller than the sectional area y--y of the connecting plate which provides a non-elastic engagement piece region, which results in the increased current density of the region in which the elastic engagement pieces are produced.
As a result of this, an elastic engagement claw region shown by a chained-line ellipsoidal portion b is heated when an excess current flows and also is raised in temperature due to generation of heat from a fusible portion. Such increased temperature of the connecting plate has an influence on the housing which stores the connecting plate therein, with the result that a portion of the housing shown by d in FIG. 7, which corresponds to the ellipsoidal portion b of the connecting plate, is deformed and discolored. In particular, if the housing is deformed, then it is difficult to replace an old fuse element with a new one and to remove the fusible link from a fusible link mounting box, which worsens the operationability of the fusible link greatly.
Also, according to the above-mentioned conventional structure, the fuse element is held at the two positions thereof by the two elastic engagement pieces respectively provided in the surface of each of the connection plates. However, such support is not always sufficient for the movement of the fuse element along the projection shown in FIG. 9, with result that the fuse element plays greatly with respect to the housing.